The Hubble Space
Telescope received a new “heart” today during a 6 hour, 48 minute spacewalk
by astronauts John Grunsfeld and Rick Linnehan. The two installed a new Power Control Unit (PCU), replacing the original unit launched with
the telescope in April 1990. The PCU serves as Hubble’s central power
switching station by distributing electricity to all systems, scientific
instruments and the Nickel Hydrogen batteries.

In addition to
eliminating an intermittent problem with the old PCU, the new unit also
is capable of handling the extra 20 percent of power output being generated
from Hubble’s newly installed set of solar panels attached during back-to-back
space walks Monday and Tuesday. Controllers at the Space Telescope Operations
Control Center in Greenbelt, MD, powered Hubble down at 3:37 a.m. Wednesday
for the first time since its launch in 1990.

Mission Specialist
Nancy Currie operated the shuttle’s robotic arm throughout the space
walk, moving Grunsfeld and Linnehan to and from various worksites on
the telescope and in Columbia’s payload bay. Grunsfeld later told Mission
Control that, “Nancy is my hero” for her work today.

Today’s space walk
started two hours late due to a water leak in Grunsfeld’s spacesuit.
After swapping the upper portion of his suit the space walk began at
2:28 a.m. Linnehan, working from the shuttle’s robotic arm, began by
removing 30 of the 36 connectors on the old PCU. He was then maneuvered
by Currie to the shuttle's payload bay where he switched places with
Grunsfeld in order to prepare the new PCU for installation. At 4:55
a.m. Grunsfeld, now working from the robotic arm, unhooked the remaining
six PCU connectors, eased the old PCU out of the telescope and carried
it to the shuttle's payload bay for return to Earth. Grunsfeld installed
the new unit at 5:53 a.m. The connectors were mated to the new PCU by
7:19 a.m. Shortly thereafter, the new PCU passed its aliveness test
at 8:02 a.m. and all functional tests were completed at 12:18 p.m.

Inside Columbia,
the flight's other space walking team, Jim Newman and Mike Massimino
looked toward the fourth space walk set to begin tomorrow at about 2:30
a.m. CST to replace the last of Hubble’s original science instruments
– the Faint Object Camera – with the Advanced Camera for Surveys.

The crew is scheduled
to awaken at 9:52 p.m. CST Wednesday. The next STS-109 mission status
report will be issued Wednesday evening, or as events warrant.

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